Rabbit recipients of artificially grown penises are eager to copulate with female partners

We've seen all sorts of tissue
engineering examples -- from bone, to brain tissue, to nerves,
to vascular
tissue, and even muscles -- but a new study from the Wake Forest
University’s Institute of Regenerative Medicine has surpassed all
of these in pure strangeness. The study used advanced tissue
regrowth techniques to create and endow lab rabbits with fully
functional replacement penises.

The research was led by
the institute's director, Anthony Atala, M.D., who is most famous for
devising a cell seeding technique that involves spraying cells
harvested from an applicable tissue onto a collagen matrix, led the
research. Under Dr. Atala's scheme the developing tissue is
bathed in a nourishing serum than keeps the tissue in a chemical
environment similar to the human body, and at a similar temperature
to that of the human body. Growth factors and other beneficial
compounds are seeded into the tissue beforehand, to encourage the
cells to divide and populate the new tissue.

Most cells
contain a wealth of information about how to grow and form their
local tissue. Once in a receptive scaffold (like the collagen),
they're sometimes able to grow and form new tissues, if they're
exposed to the proper chemicals and physical conditions. By
combining one or more tissue types and encouraging the growth of
blood vessels, organs can be formed.

Dr. Atala's team had
already regrown and implanted seven human male bladders, a
significant success. Ten years later, the patients are still
showing good function. However, the penis proved a much more
elusive and complex tissue to grow. Growing the outer skin in
theory wouldn't be overly challenging, but the inner spongy tissue,
called corpus cavernosa, proved to be a much stiffer challenge due to
the complex mix of cell types needed.

Past artificial penises
grown at Wake Forest were taken off the drawing board after failing
to stay erect when implanted into rabbits with a piece of their
spongy tissue removed. After close to 18 years of failed
attempts, the researchers tried a different angle, removing the
entire spongy tissue (not just a segment) and using different growth
factors on a complex mix of cells, including smooth muscle cells and
endothelial cells -- the cells needed to form the arteries needed to
bring blood to the penis's spongy tissues, allowing it to become
erect.

The result was a resounding success. Writes the
research team in their paper on the accomplishment, "This
technology has considerable potential for patients requiring penile
construction."

The resulting penises were identical to
their natural kin in response to electrical and chemical stimuli.
And the recipient rabbits proved eager to copulate, with eight of the
12 rabbits with implants achieving ejaculation and four becoming
fathers. While rabbits normally like to procreate over the long
term, the recipients proved unusually randy, attempting to procreate
much faster than normal male rabbits.

Describes the team,
"Most control rabbits did not attempt copulation after
introduction to their female partners. All rabbits with
bioengineered neocorpora attempted copulation within one minute of
introduction."

The study was reportedly published in the
journal Proceedings of the National Academy of Sciences (PNAS)
on Monday, though a quick
glance at the November 9 early edition did not show the study.

The research proves eerily similar to the frequently on-point
animated show South Park's episode "Eek a Penis", which
aired last year and involved the character Mr./Mrs. Garrison having
his/her penis regrown on a lab rat. Despite the success,
though, such more advanced sex change operations remain out of reach,
as scientists have yet to engineer functional testicles from body
tissues. Still, for some with damaged penis tissue, this study
may provide new hope.

The research team next plans to start
trying to implant regrown human penis tissue. States Dr. Atala,
"We're going to be doing that experimentally at our center."

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